The present invention relates to rangefinding/autofocusing devices provided in various optical apparatuses for automatically carrying out pattern recognition and optical measurement etc. in the field of optical information processing and optical sensing technology.
Conventionally, various types of the autofocusing devices have been developed for facilitating handling of pick-up instruments such as a photographic camera and CCD camera. These include, for example, one type utilizing ultrasonic emission to measure a time delay of reflection, and another type utilizing infrared radiation to measure a reflected radiation intensity. However, another interesting type of autofocusing device is based on optical triangulation to effect rangefinding and autofocusing.
The optical triangulation method is advantageous in precisely carrying out rangefinding/autofocusing over a relatively wide range from a far distance to a near distance. The typical triangulation method of the prior art utilizes a pair of CCD cameras for concurrently picking up an object such as to measure an offset between barycenters of respective pictures of the same object. For example, if the barycenter offset coincides with a span between centers of imaging lenses of the respective CCD cameras, the object is determined to exist in a far infinitive distance. Without regard to whether an image of the object is accurately focused on a photoelectric conversion plane of CCD, the distance of the object can be precisely calculated relative to the CCD photoelectric conversion plane based on geometric parameters including a span between imaging lens centers of the CCD camera pair and a spacing between the CCD imaging lens center and the CCD photoelectric conversion plane, unless the object image is seriously out of focus.
However, the conventional rangefinding/autofocusing device of the triangulation type has a drawback in that the instant calculation of the barycenter of the object image is practically difficult when using a simple processor. Generally, the object image or picture is represented in a gray level scale which requires a vast amount of calculation steps to determined the barycenter of the picture. For example, if the object picture is comprised of 480.times.512 pixels in 16 gray levels, computation must be executed for about 4.times.10.sup.6 data. Therefore, to be practical, the original picture is once subjected to binarization process, and then the barycenter is calculated according to the binarized picture. Even if such a provisional treatment is adopted, the computation must be undertaken for each of about 2.5.times.10.sup.5 points contained in the picture comprised of 480.times.512 pixels. In the conventional rangefinding/autofocusing device of the triangulation type, the computation is quite complicated to determine the picture barycenter, thereby causing one problem that a costly processor would be required to execute fast computation.
The conventional rangefinding/autofocusing device of the triangulation type has another problem such that an object cannot be automatically discriminated from a background in order to effect selective rangefinding and autofocusing. Therefore, in the conventional device, the operator has to manually align a reference or finding mark to an object, and then the rangefinding and the autofocusing are effected.